Jakarta, located in a lowland delta area with close to 50% below regional water level, is vulnerable to coastal and river flooding due to monsoons, sea-level rise and insufficient and faulty drainage infrastructurexxxiv. The rapid rates of land subsidence play a key role in relative sea- level rise: estimates suggest an average subsidence rate of 40 mm/year, in some places up to 20 cm/year. An estimated 90% of North Jakarta is expected to lie below sea level in 2030 and the 13 rivers and canals of Jakarta are projected to stop flowing freely to the sea around 2025 if no measures are taken. As the sea-level rises, saltwater intrusion of groundwater tables also becomes a problem. This is related to the high volume of groundwater extraction, with additional pressure from construction and natural consolidation of sedimentary layers. Greater Jakarta has prepared a policy for disaster management as well as the Jakarta Coastal Defence Strategy and Flood Mappingxxxv. Jakarta is also preparing a Sea Defence Wall Master Plan to protect the Northern Jakarta from inundation caused by increase in sea level and land subsidence and is now pursuing the development of a larger adaptation strategy.
A set of measures are planned to minimize land subsidence, including limiting groundwater extraction, providing sufficient supply of raw water from surface water, developing water retention basins, and building absorption wells called biopores (1 million planned). The restriction on groundwater extraction, decreed by regional regulation, is a key measure for slowing down land subsidence. The Northern Jakarta area is mandated to have 100% water-supply coverage and 0% groundwater abstraction by 2015. The rest of the city will also see groundwater extraction phased out in geographic bands moving southward by 2020, 2025 and 2030, with the similar assumption that piped water will be provided in all districts by 2030. This initiative is co-financed by taxing groundwater consumption and is supported by development of alternate water supply piping for large industrial users or relocation of large groundwater users outside the ‘critical zones’, but it admittedly still faces some challenges of proper enforcement. Other initiatives include construction of East Flood Canal and interconnection canals; Jakarta Emergency Dredging Initiativexxxvi of vital waterways (currently at 30% capacity partly due to clogging by high volume of improperly disposed solid waste); reconstruction of pumps; protection of natural coastal defences (mangroves); construction of sea embankments; and resettlement of illegal housing along rivers and lakes.
Reasons for success
Jakarta’s mitigation of land subsidence is driven by international assistance and sharing of lessons learned with other delta cities, as well as acknowledgment of the need for an integral water management approach, in which sanitation, wastewater treatment, surface water quality, alternate access to clean drinking water and flood protection are being improved in an interconnected way.
When/why a city might apply an approach like this
This approach is particularly relevant if a city has a significant portion of land at, or already below, sea level, is highly canalized, or has high rate of groundwater extraction and the delta is no longer naturally being reinforced with sediment.
C40 Good Practice Guides
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All references can be found in the full guide.